Telephone system



Feb. 16, 1937.

E. WOCHINGER TELEPHONE SYSTEM Filed July 8, 1955 6 Sheets-Sheet 1 INVENTOR. EDUARD WOCHINGER ATTORNEY.

Feb. 16, 1937.

E. wocHlNGER 2,070,876

TELEPHONE SYSTEM Y Filed July 8, 1955 6 Sheets-Sheet 2 INVENT OR. EDUARD WOCHI NGER ATTORNEY.

E. wocHlNGER l 2,070,876 TLPHONE SYSTEM Feb. 16, 1937.

Filed July a, 19:55 e sheets-sheet EDUARD wocHlNGER 3f BY ATTORNEY.v

Feb. 16, 1937. E. woczHlNcs-ERQ4 TELEPHONE SYSTEM Filed July 8,. 1935 6 Sheets-Sheet 4 INVENTOR. Y EDUARD WOCHlNGER 1% Z M ATTORNEY.

Feb. 16, 1937.

E. WOCHINGER TELEPHONE SYSTEM Filed July 8, 1955 6 Sheets-Sheet 5 INVENTOR. EDUARD WOCHI NGER ATTORNEY.

Feb. 16, 1937. E, WOCHlNGER 2,070,876

TELEPHONE SYSTEM INVENTOR. EDUARD WOCHINGER ATTORNEY.

Patented Feb. 16, 1937 UNITED STATES TELEPHONE SYSTEM Eduard Wochinger, Berlin, Germany, assigner to Siemens & Halske Aktiengesellschaft,

Siemensstadt, near Berlin, Germany Application July 8, 1935, Serial No. 30,379

In Germany lIuly 13, 1934 7 Claims.

The present invention relates to telephone systems withrmain and subsidiary exchanges and automatic operation. In thesesystems the determination of the call direction in which a de'- sired call is to be set up frequently takes place after the transmission of a varying number of impulse trains. For example, the discrimination of the call direction may take place after only one impulse train if the call is directed to a zone whose connecting lines are led oi from the rst numerical impulse receiver at the main exchange. If'on the other hand the call is to remain in one of the exchanges within the region governed by the main exchange the discrimination of the call direction may take place only after two, three or still more impulse trains.

The present invention aims at increasing the eniciency of these systems by making the devices for discriminating between call directions as simple as possible. This is achieved in that a selector, arranged in the main exchange, which determines the call direction after having received one or more impulse trains, is brought back automatically to the normal position after each of the impulse trains which do not complete the determination of the call direction, and is set again from the normal position by the next impulse train.

In Figs. l, 2, and 3 a system with main and subsidiary exchanges is illustrated as an embodiment of the invention, while Figs. 4, 5, and 6 are a modification thereof. Fig. 1 shows the devices arranged in the subsidiary exchange U. A., and

Figs. 2 and 3 show those in the main exchange H. A. The switching arrangements of the system enable the establishment of outgoing and incoming calls (exchange calls) and also of internal calls. In order to be able to set up these calls, in addition to the selector DB40 which serves as a call nder for outgoing calls and as a nal selector for incoming calls, an auxiliary selector LII/'40' is provided in the subsidiary exchange which is used as a nal selector on setting up internal calls. This selector isconnected with the main exchange over a special connecting line and is there connected to the connecting line seized by the calling subscriber when an internal call is set up. The differentiation between outgoing calls (exchange calls) and internal calls results from dialling special characterizing numbers which so operate a characterizing switch in the main exchange that this switch is operated from the normal position by each impulse train.

Outgoing tralic When the subscriber AI removes his receiver and operates key BL, the following circuit is set up: earth, key Bl, wiper al' of selector DB40, winding I of relay U41, lead al of the connecting.V line contacts 415040, 4!9an40 502x40, winding I of relay X40, wiper dII40 in position 0, resistance Wi3l`, battery, earth. Relay X40 locks up over its contact 492x110. By closing contact cidre@ the following circuit is completed: earth, magnet WM, contact 404u4l, lead bl, contacts MSc/40, irl, 1132040, 4361/40, relay KBB, bat? tery, earth. In-this circuit the magnet W41 and relay Kl energize. The selector in the subsidiary exchange thus makes one switching step. By the closing of contact 4`40lc40 magnet D40 (wipers dIdl-dIV40) is also operated so that the selector in the subsidiary exchange and the switching device in the main exchange take one switching step synchronously. Relay Y40 is switched on over contact 444d40 of magnet D40 and interrupts at contact 4361/40 the energizing circuit for magnet W4! passing over the b-lead. Moreover, relay X40 is also deenergized, so that by opening contact 440Jc40 magnet D40 is also deenergized. By the opening of contact 444d40 relay Y40 is deenergized and thus a new energizing circuit is set up for magnet WM in the subsidiary exchange. 'I'hroughithe re-energizing of relay K40 magnet D40 is also now energized once more. Thus mutual interaction continues until the calling subscriber isrreached through selector DB40 in the subsidiary exchange. Since in the present case the calling subscriber is connected to the rst contact, both the switching devices are only advanced one step. By the energizing of relay Y40 which occursatter each switching step relay P40 is connected each time to lead al so that on reaching the calling subscriber the following circuit is set up: earth, battery, relay P40, contacts 5041/40, 5033340, 4'I9om40, M5040, lead al of the connecting line, winding I of relay U4I, wiper al of selector DB40 in position I, subscriber AI, Wiper bl of selector DB40 in position I', winding II of relay U41, contacts 402u4l, 400w42 (I--ID earth. By closing its contacts43'lp40 relay P40 holds relay Y40 energized so that no further inuencing of the switching device can occur. In the testing circuit described above relay U4! also energizes in the subsidiary. exchange and at contact 403u4| switches through the connecting line to the main exchange, while through opening contact 404u4'l magnet W4! is disconnected. By the closing of contact455p40 relay J40. is energized. By the closing of contact 4221140 the loop to the connecting devices in the main exchange is closed, thus causing a connecting device to be seized by a pre-selector as in the case of an individual subscribers call. When the calling subscriber receives dialling tone he can begin to dial.

On operatingthe dial, relay P40 in the main exchange, which serves as a testing relay in setting selector DBM), is deenergized according to the impulses, whereupon the impulses are transmitted tothe connecting devices of the main Lso exchange through contact 4221740. On the rst deenergizing of relay P40 relay V40 is energized over Contact 4571240 and holds up during the impulse train since it is a slow-acting relay. The choke coil Dr42 is short-circuited by the closing of contact 4201140 so that by the simultaneous disconnection of the condensers in the speaking leads by the opening o-f contacts M6940 and 4251240 the impulse emission is maintained free from distortion. It should be noticed that throughout the emission of the impulses relay U4l in the subsidiary exchange andrelay Y40 in the main exchange are kept energized.

Until it has been established that an outgoing call is proceeding, the characterizing switching device (wipers dz'I40-di'IV40) operated by the magnet Di40 is operated in step with the setting of the connecting devices in the main exchange, magnet D140, since during the impulse emission relay J40 is kept energized over contact 4451146, being operated over the following circuit: earth, battery, switching magnet D240, contacts 459140, 458.240, 4511240, 45540, earth. If now, for example, the digit first dialled is different from the internal characterizing digit, relay V40 deenergizes and opens contact 4461140, thus deenergizing relay J 40, so that now relay VF40 is operated over wiper Dz'IV40 (earth, battery, relay F40, contacts 464h4l, 465140, wiper diIV40' (I-l l), earth). Contact 445140 prevents relay J 40 being operated again when the next impulse train is transmitted, so that the characterizing switching device is brought to rest.

The further impulses are extended in a similar way from relay P40 through contact 4221946 to the connecting devices in the main exchange, but now the characterizing switch in the main exchange is no longer influenced. After setting the connecting devices the desired subscriber may be rung by any desired means, with which we are not concerned, and conversation thus established.

On terminating the conversation, a metering impulse is transmitted to the meter of the calling subscriber, which is connected up in the main exchange through Wiper dII40 of the switching device in the main exchange which is moved synchronously with the selector DB40 in the subsidiary exchange when the latter is set. During the metering impulse occurring over the c-lead, the connection is maintained, even when the calling subscriber replaces his receiver, in that relay Y40 which is connected in the c-lead is maintained energized over its winding II during the metering. The circuit flowing over the c-lead is only broken after the metering has been completed. It may be broken in any desired way. Relay Y40 thus can deenergize and, after the receiver has been replaced at the calling station, which causes relay U4! to deenergize and hense inter alia contact 404u4 to be closed, the following circuit serving to advance selector DB4!) in the subsidiary exchange is closed by the closing of contact 435y40: earth, magnet Will, contact 4441/41, lead bl of the connecting line, contact M3040, wiper dIV40 in positions l-l I, contacts 432e40, 4361/40, relay K40, battery, earth. Selector DB4!! in the subsidiary exchange makes one switching step and by the closing of contact 44%40 the magnet D40 in the main exchange is operated so that this switching device is also advanced by one step. As in the case of setting up the connection of the calling subscriber with the main exchange, the switching device in the main exchange controls the switching device in the subsidiary exchange. Both advance to position i i under the influence of relays K40 and Yl. In this position relay E40 is operated over wiper dIII40 and contact 41540. By closing contact 43le40 relay K40 is connected to lead b2, it being disconnected from lead bl by the opening of contact 432640. By the opening of contact 438e40 the magnet D40 is disconnected from the automatic impulse circuit, and the magnet D140 of the characterizing switching device is connected to the latter by the closing of contact 435)@40. The magnet W42 of the auxiliary selector LW40 is now energized over lead h2, whereupon relay K4 is inuenced simultaneously in the main exchange. The magnet D140 thus receives an impulse over contact 4407c40 so that by closing contact 443dz'45 relay Y40 is energized and the advancing circuit for the auxiliary selector LW40 in the subsidiary exchange is again opened at contact 4341/40. By this interaction both switching devices are advanced synchronously to position Il. In this position relay H40 is now energized over: earth, wiper dil/40 in position ll, Contact 4l51/4, relay H40, battery, earth. By the opening of contact 403h40 winding II of relay X49 is disconnected, and by opening contact 44ih40 the magnet D140 of the characterizing switch is disconnected from the automatic impulse circuit. The magnet W42 in the subsidiary exchange is now operated alone, without the magnet D2'4il in the main exchange being operated, through the reciprocal play of relays K4!) and Y40, in a corresponding way, until the wiper a2 in the subsidiary exchange reaches position Il. In this position earth is connected to the a2 lead, so that the following circuit is set up: earth, wiper a2 of auxiliary selector LVS/4Q in position Ii, winding I of relay U42, lead a2 of the connecting line, contact 505km, resistance WiSl, battery, earth. Relay U42 energizes and disconnects the magnet W42 at contact 4MM/42. This is associated with the deenergizing of relays K40 and Y40, so that by the opening of contact 4751/40 relay H40 is deenergized. By the opening of contact 50571.40 winding I of relay U42 is deenergized, and by the closing of contact 44l7z49 the magnet D140 of the characterizing switch is again connected to the circuit which is influenced by contact 4407544. The magnet W42 sonnected over contact 4i0u42 is now operated, as is also the magnet Dit!) by way of relay Kilt, so that both switching devices make one switching step and thus move together into the normal position. Through relay Y4il, which is operated after the switching step over-contact 44301140, relay H40 is again operated after the switching step has been taken over the circuit: earth, wiper dz'ii in position 0, contacts 417640, 5i3x4i, 4161/40, relay H40, battery, earth. The locking circuit is then completed over: earth, contacts 5l2h40, 4761/40, relay H49, battery, earth. By the opening of contact 4l8h4 relay E40 is deenergized so that by contact 439640 the magnet D140 is disconnected and thus the connection of magnet D40 is prepared at contact 436010. Then after the deenergizing of relay Y40 on account of the opening of contact 4407c40 selector DB40 in the subsidiary exchange is advanced into position Il, in that magnet W 4i is energized in series with relay KM over: earth, magnet W41, contact 404u4l, lead bi, contact 4I3c40, wiper dIV40, contacts 432e40. 4341/40, relay K40, battery, earth. Relay Kili! again operates relay Y40 over contact 4401040, so that by the opening of contact 43E/J4!) both -relay K40 and the magnet W41 are deenergized.

Through this interaction the selector DBM) is thus advanced to position |11. In this position earth is connected' to lead al over Wiper al, so that relay U4i energizes over this lead and by opening contact 4041141A deenergizes the magnet Wfti and relay Kili). On account of contact 44i3lc40 being held open relay-YM) is deenergized and hence alsorelay H40 (contact 416y40). By the closing of contact 44ih4 magnet D40- is connected to the automaticV impulse circuit. Meanwhile relay U4! is again deenergized by the opening of contact 5051140 soithat over the bl lead the selector DB40 in the subsidiary exchange takes` the last switching step together with the switching device, which is operated by magnet D40. Since wiper dIV40 has now left the segment l-l l, further advancement is prevented. Only now can a new seizure of the connecting line take place.

Incoming traffic IfV a connection with a subscriber of` the subsidiary exchange is, desired from the main eX- change, seizure of a connecting line leading to the subsidiary exchange by a nal selector of the main exchange over the testing lead (cl, c2, etc.) corresponding to the desired subscriber is only possible when wiper (i140 is in the ncrmalposition. In this case the nal selector tests, assuming that subscriber Al is wanted, over the test lead cl, resistance W1'34, contact 410040, relay A1140, wiper 01140 in position i3, Contact 4i4a1140, resistance W1`35, battery, earth. Relay A1140 energizes in this circuit and by closing Contact 4'i3a1145 locks up independently of wiper (i140. By the opening of Contact 40a1140 battery is disconnected from the al lead so that a seizure of the connecting line on the part of the subsidiary exchange is prevented. Relay KM) is connected to the bl lead of the connecting line at contact m1611240 and hence the following circuit is set up: earth, magnet WM in the subsidiary exchange, contact 404ml, lead bl, oontacts 413040, 421110140, 432640, 4361140, relay X40, battery, earth. Magnet W4! and relay K4@ are energized in this circuit. By the interaction, as has already been described in the case of outgoing traic, a synchronous advancement of the selector D13-40 by magnet WM in the subsidiary exchange, with the switching device in the main exchange by magnet D40-which is operated over contact 4407940, is effected. Both switching devices are advanced until relay C40, which is connected to wiper CLIM over contact 44201140, reaches the test lead ci seized by the nal selector. In the case considered this happens after the rst switching step. By the energizing of relay C40 a further operation oi magnet W4! is pre Vented by the opening of contact M3040, and hence also, since relay KAB cannot energize again, magnet D40 in the main exchange is prevented from being inuenced. Leads al and bl are switched over on to the speaking leads of the nal selector by the closing of contacts 492040 and M4040. Relay A7140 is locked up, by the closing of contact 469049, over the following circuit: earth, resistance Wz'32, contact M0040, relay Andi), Contact 4l3a1140, resistance W1`35, battery, earth. The ringing current for calling the desired subscriber may be transmitted from the nal selector of the main exchange in any desired manner. When the desired subscriber replies relay Ufll energizes over the leads ai `and bl and the potential at the final selector, and switches the bl lead through over contact403u4 l.

Ringingcurrent iscut off inthe known way. The desired subscriber is now connected to the final selector ofv4 the main exchange just as a normal individual subscriber.

When theV conversation has nished, the ci lead is cut off from they final selector in any desired way, so that relay C40 deenergizes. By opening: contact 460040 relay A1140 is also deenergizedc. In the subsidiary exchange relay UM' is. deenergized. so that the magnet W4I is again connected to bl lead of the connecting line over contact 404ML The return of the switching devices tothe normal position now takes place in the same way as has been described in the case off the release of outgoing tralic.

Internal calls The seizure of the connecting line leading to the main exchangeV by the calling subscriber A! is-.accc-rnplished inthe same way as has been described for'outgoing trailic. In order to reach a subscriber attached to the same subsidiary eX- change the subscriber A! must dial the complete normal number of this subscriber. In the present example the `number 2419572 is chosen as the number of the desired subscriber A2. As mentioned" above, after connecting the calling subscriber Al to the connecting line by the energized relay P40; relay J40 is energized over contact 4501940, Wiper dz'IIlllEl` in position 0 and contact 45540; andI holds up during the individual irnpulses over contact 4461140 of relay V40 which iS energizedduring the impulses.

Subscriber Al thus first sends out two irnpulses, and hence by the operation of the corresponding contactsof relay P40, which previously operated as testing relay, magnet D140 (impulse contact 4511140) is energized twice and accordingly advances the corresponding switching de Vice'by two switching stepswhilst the seized connecting device of the main exchange likewise re ceives two impulses through Contact 4221740. When relay V40 deenergizes at the end of the impulse trainrelay J40 holds up over: earth, battery, relay JM), contact 445340, wiper diIIIl in position 2, contacts 5017142, 4537143, 4527144, winding I of` relay HM, earth. In this circuit relay HM energizes and Operates relay F40 over contact 463ML and also locks up over its windingrII by closing contact 4681141. By the closing off contact 462140, magnet D140 receives an impulse; so that the characterizing switch takes one switching` step. Hereupon magnet D240 opens its contactllclilil` so that relay F40 deenergizes. After the switching step has been taken and magnet Dillll is again deenergized by the opening of contact 452240 so that contact 46 ldifll isagain closed, relay F40 is again operated and causes the characterizing switch to be advanced again. This stepping is continued until the characterizing switch has reached the zero position, since in thiscasewiper d1'IV4il has left the contact segment I-H and hence relay. H4! is deenergized. Relay F40 is prevented from energizing by the opening of contact 4S3l14l. In the zero position cf the characterizing switch relay .14d again energizes over wiper diIII40. This operation just described occurs during theV pause between two impulse trains. It may also be mentioned that in position. H of wiper diIIiS, during the advancement `of the characterizing switch, relay H42 is operated and locks up over` contacts 4847142, 489ML and 4001/40. Thus after the return of wiper cZiII40 to position D, relay U40 is operated over contact 5007142, and is held in a locking circuit independently of wiper diII40 by closing contact 49'lu40.

By dialling the second digit4 the characterizing switch is brought to position 4. After the opening of contact 4451140 relay J40 holds up over: earth, battery, relay J40, contact 445140, wiper dz'III40 in position 4, contacts 50Bh42, 453111,43, 45271.44, winding I of relay Hll, earth. Relay H4! energizes in this circuit, locks up over contact 4t0`h4| and, as has been described above, causes the operation of the magnet Di40 of the characterizing switch. This is then brought to the normal position by the alternate operation of relay Fli. When wiper diII40 again comes to position li, relay H43 is operated over: earth, battery, relay H43, contacts 48'lh44, 5l4u40, wiper dz'IIli in position Il, earth. By the closing of contact 4831143 relay H43 locks up. Relay U40 is deenergized by the opening of contact 50lh43.

When the calling subscriber dials the third digit which consists of one impulse, the characterizing switch stands on the rst contact after the train has passed. The following circuit is set up: earth, battery, relay J40, contact 445140, Wiper dz'IIIli in position l, contacts 454h43, 452h44, winding I of relay HM, earth. By the energizing of relay H4I relay F40 is again operated and brings the characterizing switch into the zero position again. During this motion, when wiper dz'II40 is in position Il, relay H44 is operated over: earth, battery, relay H44, contacts 482h43, 5Hh45, 508u40, wiper dz'II40 in position il, earth. By closing contact H44 relay H44 completes a locking circuit for itself independent of wiper dz'II40. In position 0 relay U40 is again operated over contacts 490h44, 498h45 and wiper diII40 in position 0 and locks up over contact 49'iu40.

In a similar manner, through the fourth impulse train (9 impulses), after relay H4! has been operated on the 9th step, relay H45 is energized on the advancement of the characterizing switch into the normal position, by relay F40 in position il, the circuit being: earth, battery, relay H45, contacts 43oh44, 50'lu40, wiper dzII40 in position l i, earth. By the opening of contact 493h45 relay Ufti is deenergized. The characterizing switch has again reached position 0.

After the fth digit has been dialled, which consists of five impulses, the characterizing switch stands on the fifth contact, so that after relay Hii has energized in this switch position, relay F40 is again energized and the characterizing switch is returned to the zero position. During this motion relay H46 is energized over wiper H1140 in the following circuit: earth, wiper diIId in position Il, contacts 508u40, 509h45, relay H46, battery, earth. By closing contact -Siz40 this relay locks up. Meanwhile the characterizing switch reaches the zero position. After the dialling of the sixth `digit which consists of seven impulses and hence moves the characterizing switch round seven steps so that its wiper reaches position seven, relay Z40 is operated over: earth, battery, relay J40, contact 445140, wiper cZiIIIlQ in position 1, contact 44!h46, winding I of relay 240, earth. By closing contact iiiiefii? relay Z40 locks up over its winding II. By the opening of contact 458240 further influencing of the characterizing switch by numerical impulses is prevented. Moreover it cannot be brought back to the normal position since relay is not operated.

When the calling subscriber dials the last digit, in the present case the digit 2, since contact 429240 is now closed this is transmitted with the help of contact 4281340 to magnet W42 over lead h2 and thus the auxiliary selector LW40 in the subsidiary exchange is set on the contact of the desired subscriber. The transmission of this impulse train to the connecting devices in the main exchange is prevented in that contact 423240 has opened the impulse circuit and moreover has thereby released the connecting devices in the main exchange. Relay R40 is brought under the iniiuence of a switching device over contacts ieli and 48%140 every three seconds, and is thereby energized, so that every three seconds ringing current is transmitted to th-e desired subscriber over lead a2 by the closing of contact 425140. The calling subscriber receives a portion of this ringing current over contact |0140 as an indication that the line is free.

When the called subscriber replies, relay P4I energizes in the ringing pause over: earth, battery, resistance Wz'ZS, contacts 429240, 4211240, winding I of relay Plil, contact 426MB, lead a2 of the connecting line, winding I of relay U42, wiper a2 of the auxiliary selector LW40 in position 2, subscriber A2, wiper b2 of the auxiliary selector in position 2, winding II of relay U42, contact 40Su42, earth. Through relay P4| relays H42 to H40 are deenergized on account of the opening of contact 489p4l, so that by the opening of contact 44H45 relay .140 is also deenergized. Accordingly relay R40 cannot be further energized over contact 495740, so that the transmission of ringing current is interrupted. In

the circuit closed when the desired subscriber re- Y plies relay U42 energizes as well as relay PAI and by closing Contact 4001042 switches lead b2 through to the main exchange. Both subscribers are connected together over contacts 4| lp4l and 424p4l, and current is fed from the main exchange. For the calling subscriber the current passes over relay P40 and the choke coil Dr4l, and for the called subscriber over windings I and II of relay Peil.

The internal call is metered in that the meter SMl connected over wiper c1114@ corresponding to the movement of the switching device DB4!) in the subsidiary exchange is energized over contacts d'lleit, 49l7'4tl and 490y40 on the reply of the desired subscriber.

When, after ending the conversation, the calling subscriber replaces his receiver, relay P40 which is inuenced over the subscribers loop deenergizes. Thereupon relays Yli and Z140 and also relay P-ii are deenergized. Relays U4I and U42 also deenergize. By the closing of contacts 4361/40 and lilludl the operating circuit for the magnet W4! in the subsidiary exchange and for relay B140 in the main exchange is closed, and thus the switching devices are released in a similar manner to that already described for the case of outgoing calls.

Had the desired subscriber not replied, relay [40 and then relay '.340 would have deenergized when the calling subscriber replaced his receiver before contact 40H49 had been closed by the deenergizaticn of relay J 4S, so that in this no metering would have taken place.

Special circuits If the selector D540 in the subsidiary exchange is displaced from the normal position by hand, earth is connected to the lead over contact istruiti and wiper of the auxiliary selector LW40 in position t, and hence relay K40 is energized in the main exchange, so that, as in the case of a subscriberscall, an operating circuit is completed over contact 4I8m40 for magnet W4I in the subsidiary exchange and for relay K40 in the main exchange. The selector DB40 in the subsidiary exchange is prevented from being released, by lmagnet W4I being held energized in this circuit, until relay K40 also influences magnet D40 in the normal way and so also advances this switching device by one step. Relay Y40 is then again cut o from the operating circuit as in the case of setting up an outgoing call, so that the selector in the subsidiary exchange and the switching device inthe main exchange are then advancedsynchronously to position II. In this position, as in the release motion for outgoing traiiic, the magnet W42 is operated and brings selector LW40 to the zero position with the characterizing switch D240, whereupon selector DBlil is advanced to position I1 independently and then moves to the zero position together with the switching device controlled by magnet D40. i

If the auxiliary selector LW40 is displaced from the zero position byhand, earth is connected over contact 40Iw42 (I-I 1) to the zero position of wiper al of selector DB40, so that in this case, as in the case of a `subscribers call, relay X40 is influenced in the main exchange. In this case also both switching devices rotate in the same way as has been described for the case of release. In order to prevent a subscriber, on removing his receiver, from causing the seizure of the connecting line, which in the case of dialling an internal call must result in a wrong selection since the auxiliary switch LW40 is displaced, earth is cut oi from contact 4021L4I by contact 4001042 (I-'I'I) so that the testing relay P40 in the main exchange cannot test on the subscribers contact.

If both switching devices in the subsidiary exchange are displaced from the normal position by hand, earth is again connected to the a2 lead so as to energize relay X40, over contact 40lu4I, since obviously relay X40 must be energized for every release of the switching devices in the subsidiary exchange because otherwise no control of those can take place over the main exchange. In this case also the earth is disconnected through contact 400w42 (I-I'I).

Thus as soon as the synchronism between the switching devices in the subsidiary exchange and the switching devices in the main exchange is destroyed, setting on a calling subscriber is no J longer possible.

If the switching device in the main exchange operated by magnet D4 is displaced from the normal position by hand the operating circuit for magnet W4I and relay E40 over lead bI of the connecting line is completed over wiper dz'IV40 in positions I--I I, so that the switching devices return to the zero position as described above. Seizure of the connecting line by a subscriber who removes his receiver at this moment cannot occur because relay X40 is not energized and accordingly the testing relay P40 is not connected to lead al of the connecting line.

If on the other hand the characterizing switch is displaced from the zero position by hand, relay Kl energizes over wiper dz'IV40 positions I-II, and connects a negative potential to lead b2 of the connecting line through contact 43Ic40 and relay K40, whereby magnet W42 is energized as well as relay K4. Both switching devices are then brought tothe zero position synchronously,

as described above. Since relay E40 is energized during this motion, even if relay X40 is energized due to a new call occurring during this motion, the selector DB40 in the subsidiary exchange can only be set aiter the return to the normal position, since for the moment contact 432e40 is still open.

In the main exchange each seizure of the con-' necting line can be indicated by the lighting of the seizing lamp L. They can also be recorded by a special device. If it is desired to record incoming and outgoing seizures separately the contacts `492:1:40 and 494an40 can each be connected separately to a recording device.

In Figs. `Ll, 5, and6 a system with a main and subsidiary exchange is illustrated as a further embodiment of the invention, in which a battery of low potential (l2 volts) is provided in the subsidiary exchange (Fig. 4) which is charged by the battery at the main exchange over a lead of fthe connecting `line `leading to the main exchange (Fig. 5). In the charging circuit a relay L50 is included which is energized in the normal condition, and if necessary further relays (L5I, L52) lin case the contacts to be provided for each subscriber cannot b-e accommodated on one relay. 'Ihese relays connect all the subscribers of the subsidiary exchange to the calling circuit,

over their working contacts, and on the deenergizing occurring when a subscriber calls, cause such a switching over oi the calling circuit that the individual subscriber can be tested. In order to have 'to provide as `few relays of this sort as possible, contacts operated mechanically by selector V1DB50 of the subsidiaryexchange, for example 650w5I (|-I'I) are -used for the same purpose, which are opened on the rst switching movement of Aselector DB50 and remain open until position II.

The subscribers are connected to the line leadingto the main exchange by selector DB50, which for=outgoing and incoming calls is controlled by a switching device (wipers dI50-dIII50) in the main exchange. .I-It thus operates as a double purpose selector. For establishing internal calls a branch line `is connected in the subsidiary exchange tothe connecting-line leading to the main exchange. With this a subsidiary selector LW50 is associated which only serves as a nal selector on setting up internal calls. Its setting for internal calls takes place directly through the dialling of the calling subscriber, in local circuits of 'the subsidiary exchange.

The differentiation between outgoing exchange calls and internal calls is effected by a characterizing switch (wipers diI50-dz'IV50) which is set by the various impulse trains, until the desired direction is characterized, in such a manner that it returns to normal position after each impulse train to be set 'again by the next impulse train.

`In the 'normal condition of the system all the switching devices in the main exchange and in the subsidiary exchange are in the zero position, so vthat the following circuit is completed over the a, lead of the connecting line: earth, battery (48 volts), resistance Wz`39, wiper 11H50 in position 0, Winding I of relay X50, contacts 5141x250, 56Slm50, 559050, lead a of the connecting line, contact 525:135I, winding I of relay U5I, contacts 523g50, 52Iu52, wiper ral of selector DB50in position 0, relays L50, L5I, L52, battery (-12 volts) earth. In this circuit which forms the charging circuit `for the battery of the subsidiary exchange, relays L50, L5I and L52 are energized. The number of L-relays is adjusted to the number of the subscribers. Relay X50 in the main exchange is not energized in the charging circuit.

Outgoing tratto When a subscriber of the subsidiary exchange, for example A!, removes his receiver, the following circuit is set up: earth, contact 5301I, winding II of relay U5!, contacts 534950, 5301/52, wiper b! of selector DB50 in position 0, subscribers line, contact 650105! (!!1), wiper a! of selector DB5!) in position 0, contacts 52Iu52, 523g50, winding I of relay U5! contact 525x5l, lead a of lthe connecting line, contacts 550050, 565an50, 510x50, winding I of relay X50, wiper 111150 in position 0, resistance Wz'39, battery, earth. Besides a transitory energizing of relay U5! relay X50 energizes in this circuit. By

i closing contact 6301250 relay X50 locks up over its winding II. By opening contact 510x50 winding I of relay X50 is disconnected from the a lead, and the testing circuit for relay P50 is prepared by the closing of contact 515551250.

The L-relays (L50, L5!, L52) in the subsidiary exchange deenergized. By the closing of contact 539150 the magnet W5! of selector DB5!) in the subsidiary exchange is connected by the b-lead of the connecting line. The following circuit is now set up: earth, contact 50011152 (!-!1), magnet W5l, contacts 539150, 538f5l, b lead of the connecting line, contacts 551c50, 503e50, 58!y50,1582h5!, relay K50, battery, earth. In this circuit magnet W5! and relay X50 are energized. The selector DB50 in the subsidiary exchange is advanced one step, as is also the switching device in the main exchange since the magnet D50 of the latter is energized over contacts 5920,50, 5051650 and 610250. Contact 5941150 is closed by the influence of magnet D50 and relay Y50 is thus energized over resistance Wi38. By opening its contact 58Iy50 this relay breaks the circuit passing over the b-lead. Magnet W5! in the subsidiary exchange and relay K5!) in the main exchange are accordingly deenergized. By the opening of contact 595lc50 magnet D50 is dcenergized, which results in the deenergizing of relay Y50 by the opening of contact 504d50. This alternation which serves to advance the selector in the subsidiary exchange synchronously with the switching device in the main exchange proceeds until the calling subscriber is reached. In the present case both switching devices are only advanced one step since it is subscriber A! who is calling. After this step has been executed the testing relay P50, is connected to the a-lead of the connecting line, this occurring after every switching step. Since the switching device DB50 is standing on the calling subscribers line the following circuit is set up: earth, battery, relay P50, contacts 516y50, 5153250, 556an50, 550050, lead a of the connecting line, contact 525x5l, winding I of relay U5l, contacts 523950, 52Iu52, wiper al, of selector DB50 in position l, subscriber AI, wiper b! in position I, contacts 535u52, 530950, winding II of relay U5! contact 530f5l, earth. Relay P50 energizes in this circuit. Over contact 5961150 it maintains winding I of relay Y50 energized, so that since contact 58ly50 is kept open further advancement of the switching device is prevented. By the closing of contact 580y50 earth is connected to lead b over the choke coil Dr52. In the testing circuit described above relay U5! is also iniiuenced in the subsidiary exchange so that relay F5! is energized through contact 509u5l, and by closing contact 53H5! in the subsidiary exchange switches through lead b to the main exchange. By the opening of contact 538)5! magnet W5! is cut oi from the b lead. The testing relay P50 and relay U5! hold up in the feeding circuit of the calling subscriber. By contact 5632950 the loop is completed in the main exchange for the operation of a preselecting device for the purpose of seizing a free connecting device. When a free connecting device is reached in the main exchange, the subscriber receives dial tone in the known way and can commence dialling.

On operating the dial the feeding circuit is interrupted intermittently so that relay P50, which was previously used for testing, is deenergized in the main exchange according to the impulses, and transmits the impulses to the connecting devices of the main exchange by its contact` 5531750. Furthermore in the first release of relay P50 relay V50 is operated over contact 50lp50 so as to effect a clean transmission of the impulses by short circuiting the choke coil D! (contact 56|c50) and disconnecting the condensers by contacts 5601150 and 5521250. Relay U5! which is in the feeding circuit remains energized during the emission of the impulses.

Until it has been established that an outgoing call (exchange call) is occurring the characterizing switch is advanced in accordance with the dialling, for on the energizing of relay P50 relay T50 has been operated over Contact 6001250 (earth, battery, relay J50, contact 598150, wiper diIII50 in position 0, contacts 000p50, 0!!x50, 5I2z50, earth), so that on the rst release of relay P50 magnet D150 is operated over contacts M2250, 5!!:c50, 60lp50 and 6l3j50. After the impulse emission relay V50 deenergizes. If two impulses have been sent out, the characterizing switch will be standing on the second contact which corresponds to internal calls, and in this case relay J50 continues energized over winding I of relay H51, the circuit being: earth, battery, relay J 50, contact 508150 wiper 2:11150 in position 2, contacts 0E0h52, 50111.53, @00h54, winding I of relay H59, earth. By the closing of contact 52|h5! relay F50 is operated, thus operating the magnet D150 over contacts MM50 and 6l5h5! which is deenergized again after the deenergizing of relay F50 on the opening of contact 5i5dz'50. After the closing of contact 0l5di50 relay F50 again energizes, so that after closing contact thi/50 magnet D250 is also again influenced. Through this interaction the characterizing switch is brought into the rest position. The interaction is repeated after each impulse train until the digit sent cutis diiTerent from the internal characterizing digit, this occurring at the latest at the sixth digit. If for example, the distinguishing digit is an 0, no matter in which impulse train out of the six impulse trains dialled it occurs the relay J50 can no longer hold up after the characterizing switch has reached contact 5 with its wiper dz'III50, so that the characterizing switch stays in this position. The connection is then extended over connecting devices in the main exchange. The desired subscriber is rung by devices in the main exchange with which we are not concerned. When he replies relay Y50 is maintained energized in series with the meter SM! corresponding to the calling subscriber, which is connected through the switching device oi the main exchange, until the metering taking place over the c lead on the termination of the call is completed. Relay Y5El which is held energized during the metering prevents a premature release in the event of subscriber A replacing his receiver during the metering.

When the calling subscriber replaces his receiver, since the feeding circuit over leads o, and b is interrupted, relay P55 in the main exchange and relay U55 in the subsidiary exchange deenergize. The latter relay by opening contact 549115! disconnects relay F55. The transitory energizing of relay G55 which then occurs is of no signicance. When the metering is completed, relay Y5D, which has held energized over the c-lead, deenergizes so that relay H5! is operated over contact i'ly. This relay by means of contact 582715! keeps the operating circuit for magnetl W5! in the subsidiary exchange and for relay K55 in the main exchange broken until the characterizing switch has reached the zero position corresponding to the motion described above under the control of relay F50 which was energized over contact 521715l. The circuit for relay H5! is broken through the `wiper dz'IVED leaving the contact segment i-I l, so that the relay releases and by `closing contact 582715! closes the operating circuit passing over the b-lead. In this circuit magnet W5! in the subsidiary exchange and relay K5ll in the main exchange are now again energized so that the selector DB5!) and the switching device in the main exchange controlled by magnet D55 are advanced synchronously as described above in the case of a subscriber calling. If during this return to normal a subscriber of the subsidiary exchange removes his receiver, as soon as the selector DB5il comes to the position to which the calling subscribers line is connected, a new seizure can take place, in which the corresponding meter is correctly connected up, since the switching device in the main exchange and the selector in the subsidiary exchange run synchronously. If such a call does not occur, relay H50 energizes over wiper (1155 when both switching devices have reached position Il (contact 5!'7Y5il is closed after each switching step) and brings the switching device in the main exchange to rest by opening contact 5527155. Relay X50 is deenergized by the opening of contact Ei3l7150.

Selector DB5!! in the subsidiary exchange is now advanced alo-ne by relays K55 and Y5 in the main exchange, in that relay K55 now causes the impulses for magnet W5! to be produced directly through relay Y5EJ, over contacts 555k55, 5937150, and H5255 without the intermediate switching of contact 59ild50. Magnet W5! is influenced under the control oi contact 58ly5 until the selector DB5@ has been brought to position l1. In this position the following circuit is now set up: earth, battery (48 volts), resistance W1'35, wiper CZII55 in position l! contacts 5737158, 514150, 566611155, 555050, lead a of the connecting line, contact 5255l, winding I of relay U5l, contacts 523955, 52l1152, wiper al in position l'l,y

relays L59, L55, L52, battery (l2 volts), earth. Relay L55 energizes together with the other L-relays. By the opening of contact 539155 the magnet W5! in the sub-sidiary exchange and also relay K5 in the main exchange are disconnected. Accordingly relay Y5i! also remainsdeenergized so that by the opening of contact 5l'ly5il`relay H50 is deenergized. By the opening of contact 5137150 the potential connected to the a lead of the connecting line is cut off, soI that now the L-relays in the subsidiary exchange again `deenergize. Magnet W5! is consequently again con-- nected to lead b of the connecting line over contact 539150. The operating circuit for magnet W51 and for relay K55 is again closed. Selector D358 thus executes one further step into the zero position. Since, however, contact 5927155 is likewise closed again, magnet D56 is also influenced again through contact 5957c5, so that the switching device in the main exchange also steps into the zero position. The switching device in the subsidiary exchange and the switching device in the main exchange thus make the last step into the zero position together. Since in the zeroposition the relays L50, etc., energize again in the charging circuit further advancement is prevented. A new seizure of the connecting line can now take place in each call direction.

VIncoming tralc A seizure of the connecting line leading from the main exchange to the subsidiary exchange by a final selector of the main exchange over the testing leads Cl, C5, etc., can only take place when wiper dIIISQ is in the zero position. If, for example, subscriber A5 of the subsidiary exchange is desired, the nal selector is set by numerical impulses in any desired manner, in such a way that it can test on lead c5. Relay A1155 is energized in the main exchange over this testing lead. By closing contact 5690.115!) relay A1155 locks up independently of wiper dIII5in a circuit passing over the testing lead c5. The calling circuit is opened at contact 55Ecm50'so that the L-relays release in the subsidiary exchange and thus the connecting line is prevented from being seized by the subsidiary exchange. By the closing of contact 539150 magnet W5! in the subsidiary exchange is connected tothe b lead of the connecting line, so that as in the case of a call proceeding from the subsidiary exchange, the operating circuit for magnet WEE in the subsidiary exchange and relay K5() in the main exchange, which passes over the b-lead, is conipleted. The selector DB5!! in the subsidiary exchange and the switching device operated by magnet D50 in the main exchange are now advanced synchronously, as has been described in the case of outgoing traffic, until wiper (Z of the switching device .in the main exchange reaches the testing lead c5 seized by the final selector. At this moment relay C50 which is connected to wiper 1115i! over contact 512611155 is energized. By the opening of contact 55'7c5il the operating circuit for the magnet, which is cornpleted over the b-lead, is broken and by the closing oi contacts 556c50 and 558c59 the speaking leads of the connecting line are switched over on to the speaking leads seized by the nal selector. Relay A7155 is connected in a new locking circuit. The desired subscriber is now rung in the known manner from the final selector. When he replies the ringing current is cut cfr" in the nal selector in the known way, whereupon relay U5! is energized over the speaking leads and the potential applied in the final selector, and by closing contact 549115! operates relay FEI. The latter relay by closing contact 53H5! also switches through the b-lead in the subsidiary exchange. The desired subscriber is now connected directly to the nal selector just as is a normal individual subscriber.

At the end of the conversation the testing lead c5 seized by the final selector is cut off, so that relay C5!) deenergizes and by opening Contact 561050 deenergizes relay A1150. By the opening CTI . be advanced to the normal position.

f 7 the characterizing switch or contacts 555055 and 558c relay U5I in the subsidiary exchange is deenergized and by opening contact 555ml deenergizes relay F5I also. By the closing of contact 538f5I the operating circuit completed over the ZJ-lead is again closed, and the selector of the subsidiary exchange is brought back to the no-rmal position together with the switching device in the main exchange, as described in the case of outgoing trac.

Internal calls When subscriber AI of the subsidiary exchange removes his receiver for the purpose of setting up an internal call, selector DB50 in the subsidiary exchange is set on the line of the calling subscriber under the control of the main exchange, in the same way as for the case of an outgoing call, so that after reaching the calling subscribers position the switching device in the main exchange which is moved synchronously with the selector in the subsidiary exchange, connects up the meter SMI corresponding to the calling subscriber, over wiper :11150. In order now to be able to reach subscriber A5 who is connected to the same subsidiary exchange, the calling subscriber must dial the complete number of this subscriber. In the present embodiment this number is taken to be 2419575.

As described above, relay J 50 is energized after the energizing of testing relay P50 in the main exchange. While the impulses are being transmitted itis held energized over contact 5991250 of relay V55 which is operated during the dialling.

When subscriber AI dials the first digit 2 the magnet Di50 of the characterizing switch is operated twice, so that the wiper of the characterizing switch moves on to the second contact. In this contact position relay .T50 is held energized in the same way as in the case of outgoing calls, and also relay H5I is operated (winding I) rIhe latter relay locks up over contact Iilhl. By the closing of contact 62Ih5l relay F50 is operated and by interaction with magnet D150 causes the characterizing switch to Before reaching the rest position relay H52 is operated in position I! over wiper diI50 (earth, wiper diI5il in position H, contacts 536u50, 535h55, 624h53, relay H52, battery, earth). This relay locks up in the circuit: earth, battery, relay H52, contacts @25h52, 558150, 639e50, earth. On reaching the normal position relay U50 is influenced over contacts 554h52 and 655h53, and locks up over contact 64Iu50. The different digits of the calling number 4, 1, 9, and 5 now operate successively on the characterizing switch and cause relays H53-H56 to be energized in position II after each return of the switching device (wiper dz'IISEi) to the normal position. The characterizing switch is thus brought back to the normal position after setting by each digit so long as this digit is not a critical one and is then in a position to be set again by the following impulse train. On dialling the penultimate digit (wiper diIII5i) reaches the '7th Contact over which, since contacts 552h55, 55h55 are closed, relay Z50 is operated and by opening contact 555250 causes a release of the connecting devices in the main exchange. Relay Z50 is held operated over its winding I over contacts 551250 and 585955. In the energizing circuit of winding I of relay Z55 relay H5! is also inuenced through its winding I and by operating relay F56 over Contact 62 Ih5| causes the characterizing switch to return to normal, the magnet D250 being controlled over contacts Elf50 and Blhl. On the termination of this impulse train relay J 50 releases and cannot be energized after the characterizing switch has returned to the normal position, since the earth is disconnected at Contact M2255. It should be noticed that before the release of relay J50 relay E55 was operated and locked up over its contact 585e50 independently of contact 59 Iz'50. At contact 583650 the earth which is connected over the choke coil D152 to the b lead during dialling is disconnected so that the loop completed over the connecting line and leading to the calling subscriber is cut oi. Relay U5I in the subsidiary exchange is thus caused to deenergize. Since relay F5I is energized, relay G50 is operated over contact 550u5I and connects earth directly to the a lead of the connecting line, over contact 521950, so that the relay P50, which was transitorily deenergized by the disconnection of earth over the choke coil D752, again energizes. Relay Y50 which is inluenced over contact 5961150 remains energized during the short interruption. Moreover, by the closing of contacts 524955 and 535950 a local circuit is completed over the loop of the calling subscriber for magnet W52 of the auxiliary selector LW50 in the subsidiary exchange. This selector thus makes one switching step but this is of no importance because no subscriber is connected to contact I. When the subscriber dials the last digit (5) the magnet W52 of the auxiliary selector LW50 is operated directly and the selector is thus set on the desired subscribers (A5) line. During the rst release of contact 5431052, relay V5I is operated, since contact 54Iw52 (I-I'I) was closed on the first switching step of the auxiliary selector LW55, and holds up during the impulse train. At the end of the impulse train relay V5I deenergizes, so that now relay X5I encrgizes over contact 552o5i and Contact 55511252 (2--II) which was closed after the second switching step. The line of the desired subscriber is now connected to the a, and b leads of the connecting line by the closing of contacts 525:55! and 533m5l. Through the previous energizing of relay E50 in the main exchange the ringing machine is set in operation over contact MM50, which connects ringing current to the b lead leading to the subsidiary exchange, every three seconds over contact 555650 so that the bell of the desired subscriber is 0perated.

If the desired subscriber does not reply and the calling subscriber therefore replaces his receiver, the magnet W52 is deenergized and consequently also relay F5I by the opening of contact 5421052. By means of contacts 529f5l and 528125I the magnet W52 rotates the selector back into the normal position with the interaction of relay V5I. After the closing oi contact 5551052 (I--I'I) in the normal position, the operating circuit for magnet W5I passing over the b lead is again closed, so that, as in the case of the release of outgoing calls, selector DB55 and the switching device in the main exchange operated by magnet D50 are released in the manner described. If the called subscriber replies relay U52 in the subsidiary exchange and relay K50 in the main exchange energize in series. Contact 5l' I7c50 transmits a metering impulse to the meter SMI of the calling subscriber, whilst by the opening of contact 595c55 relay E50 is deenergized and the ringing current is thus cut off. After the opening of contact 584e50 relay K50 holds up over contacts 586250 and 585lc50 until relay G50 has deenergized by the opening of contact 541u52 in the subsidiary exchange and hence the direct earth is disconnected from the a lead at contact 5219'50. Relays K50 and P50 deenergize, but only transitorily in the case of P50. As soon as contact 519lc50 has connected earth to the b lead over the choke coil Dr52, relay P50 again energizes so that a release of the call is prevented. Contacts 522u52 and 53111.52 in the subsidiary eX- change maintain the calling and called subscribers connected in parallel, both subscribers obtaining their feeding current over relay P50 and the choke coil Dr52 in the main exchange.

The release of the connection only occurs when both subscribers have replaced their receivers, for then in this case relay P50 deenergizes, so that relay Y50 is also deenergized by the opening of contact 5901150, and closes the operating circuit for magnet W5I in the subsidiary exchange again at contact 58|y50. Thus selector DB50 is switched into the normal position synchronously with the switching device operated by magnet D50 in the main exchange, in the manner already described.

During the return motion a fresh Seizure from the subsidiary exchange is possible, whilst a seizure from the main exchange is prevented so long as the switching device operated by magnet D50 is away from the normal position. The release of the auxiliary selector LW50 has already been described for the case in which the desired subscriber does not reply. It takes place after the deenergizing of relay F5I in the circuit: earth, contacts 529f5l, 528115! (control contact), magnet W52, battery, earth.

Special circuits If selector DB50 in the subsidiary exchange is displaced from the zero position by hand the L- relays deenergize so that the operating circuit is closed over contact 539150 for magnet W51 in the subsidiary exchange and for relay K50 in the main exchange. By the closing of contact 505lc50 in the main exchange magnet D50 is operated and the switching device is thus advanced one step. Both switching devices are now returned to the zero position in the known way. During this return motion seizing cannot take place since relay X50 has not been energized so that the testing circuit is not prepared at contact 515x50.

If the auxiliary selector LW50 is displaced from the zero position by hand, relay V5I energizes over contact 5401052 (l-l'l) and connects magnet W52 in a local circuit over contacts 520f5l and 528'05! which is alternately broken and closed by relay V5I.

If the switching device in the main exchange operated by magnet D50 is displaced from the normal position by hand, the L-relays in the subsidiary exchange are deenergized and connect magnet W5I to the b-lead, so that again selector DB50 and the switching device operated by magnet D50 in the main exchange are brought to the zero position. In this case also seizure from the subsidiary exchange during the return motion is not possible.

If the characterizing switch is displaced from the normal position by hand, relay HEI energizes over wiper diIV50 and advances this into the normal position by means of relay F50 energized over contact 62Ih5| by interaction with the characterizing switch magnet Di50.

Each seizure is indicated at the main exchange by a seizing lamp L. Each seizure can also be recorded by the connection of a recording device. If it is desired to record incoming and outgoing seizures separately the contacts 630:1:50 and 632111150 are connected to separate recording devices.

What is claimed is:

1. In an automatic telephone system, a main exchange and a sub-exchange connected by a trunk line, a register switch in said main exchange for determining when a call originated by a sub-exchange subscriber is to be routed back to the sub-exchange, means for operating said register switch from normal position each time a series of impulses is transmitted over said trunk line from the sub-exchange in response to a subexchange subscriber making a call to another subscribers line, and means for automatically resto-ring said register switch to normal position aftereach series of impulses which do not determine that the call is to be routed back to the subexchange.

2. In an automatic telephone system as claimed in claim 1 including registering means associated with said register switch, and means for operating said registering means during each release of said register switch to register the value of each transmitted series of impulses.

3. In an automatic system as claimed in claim l including means for preventing the automatic restoration of said register switch in response to the receipt of the series of impulses which determines that the call is to be routed back to the sub-exchange.

4. In an automatic telephone system as claimed in claim 1 including discriminating means operated in accordance with the diierent positions said register switch has been operated to for enabling the call to be routed back to the sub-exchange.

5. In an automatic telephone system as claimed in claim 1 including switching means operated in accordance with the positions said register switch has been operated to for enabling the call to be routed to the sub-exchange, and a nal selector in the sub-exchange thereafter operated in accordance with a subsequent series of impulses to complete the call to a called sub-exchange subscribers line.

6. In an automatic telephone system as claimed in claim 1 including switching means operated in accordance with the positions said register switch has been operated to for enabling the call to be routed to the sub-exchange, a nal selector inthe sub-exchange thereafter operated in accordance with a subsequent series of impulses to complete the call to a called sub-exchange subscribers line, and an impulsing relay in the main exchange for controlling the operation of both said register switch and said iinal selector in accordance with the series of impulses transmitted over said trunk line.

7. In an automatic telephone system as claimed in claim 1 including a second trunk line connecting said exchanges, a switching means operated in accordance with the positions said register switch has been operated to for enabling the call to be routed back to the sub-exchange over said second trunk line, and a nal selector in the subexchange thereafter operated over said second trunk line in accordance with a subsequent series of impulses to complete the call to a called subexchange subscribers line.

EDUARD WOCHINGER. 

